UN High Commissioner for Human Rights Louise Arbour said she had appealed directly to Iraqi President Jalal Talabani, saying her concerns about the fairness of Saddam Hussein's trial also applied to his co-defendants.

Under international law the men should have the chance to seek a pardon or have their sentences commuted, she said.

But Mr Askari told the BBC's Arabic service: "Nobody can stop the carrying out of court verdicts. The court's statute does not allow even the president of the republic or the prime minister to commute sentences, let alone grant a pardon.

"Therefore, no pressure can stop the executions."

Ms Arbour made a similar appeal before Saddam Hussein's execution, which took place before dawn on Saturday.

Saddam Hussein, Barzan and Bandar were sentenced to death over the killings of 148 Shias in the 1980s.

Footage investigation

Mr Askari also said two guards employed by the ministry of justice - which is responsible for carrying out of verdicts and death sentences - were being questioned about the taunting of Saddam Hussein as he stood at the gallows, and the unauthorised mobile phone images that were taken.

We will take care of all the loopholes of what happened during Saddam's execution

Mowaffaq al-RubaieIraqi national security adviser

"The number of people who had mobile phones... has been identified. There is an arrest warrant for two of the guards who took part in the execution of the dictator Saddam. They are being questioned," he said.

Iraqi national security adviser Mowaffaq al-Rubaie has told the BBC that lessons have been learned from the incidents and future executions will be handled differently.

"We will take care of all the loopholes of what happened during Saddam's execution and we will leave no stone unturned to pursue those who have spoiled the victory of the Iraqi people in executing Saddam Hussein," he said.

On Wednesday, the Iraqi government began an investigation into the taunts and the unofficial footage, which appeared on the internet hours after the execution and showed the moment of death.

The authorities released official footage of Saddam Hussein's execution to prove to the public that he was dead. But that film did not include any sound and did not show the actual moment of death.